1. Field of the Invention
The invention relates to a filter cartridge for cleaning oil of an oil sealed vacuum pump. The cartridge is releasably fastened to the vacuum pump and contains filter materials. Filter cartridges of this type are included in the oil circuit of the vacuum pump and oil flows continuously through them. The oils employed in vacuum pumps may be mineral oils, synthetic lubricants, e.g. perfluorated hydrocarbons or the like.
2. Discussion of the Prior Art
A filter cartridge of the above-mentioned type is disclosed in German Utility Model Patent No. 83 29 813. This prior art filter cartridge contains an adsorption agent, i.e. activated aluminum oxide, as its filter material. This filter material is suitable for removing oil fatigue products and polar impurities from the liquid lubricant of the vacuum pump by chemical effects. Additionally, the grain size of the filter material is selected to be so small that it is possible to catch solid particles down to a grain size of 1.mu. through mechanical effects. In using the prior art filter cartridges it has been found that the filter layer builds up a relatively high resistance in a relatively short time so that a bypass valve opens. The bypass valve is customarily included in the prior art filter cartridges. With an open bypass valve, the liquid lubricant flows through the pump circuit in an unfiltered state.